The present invention relates generally to gas turbine engines, and, more specifically, to turbine rotor blades therein.
In a gas turbine engine, a plurality of turbine rotor blades are mounted around the perimeter of a rotor disk and receive combustion gases from a combustor for extracting energy therefrom and powering the rotor disk. Since the blades are subjected to hot combustion gases during operation, they are typically cooled by providing cooling circuits therein which receive a portion of pressurized air bled from a compressor disposed upstream from the combustor.
The first stage turbine blade found in the high pressure turbine mounted immediately downstream of the combustor receives the hottest combustion gases and therefore requires the greatest amount of cooling for ensuring a useful life. Each blade includes a dovetail which removably mounts the blade to the rotor perimeter, with an airfoil having pressure and suction sides extending radially outwardly from the dovetail. One or more air inlets are provided in the dovetail and are suitably joined in flow communication with the compressor for receiving a portion of the air therefrom for use in cooling the airfoil. The airfoil includes various cooling circuits therein which circulate the cooling air from root to tip of the airfoil and between leading and trailing edges thereof.
The airfoil includes various apertures or holes through the pressure and suction sides for discharging the cooling air typically as a film for providing film cooling to protect the outer surface of the airfoil from the hot combustion gases flowable thereover. The airfoil typically includes holes in its tip which also discharge a portion of the cooling air. Some of the tip holes are center mounted between the pressure and suction sides and are relatively large in diameter for allowing any dust contained in the cooling air to be withdrawn from the airfoil without clogging the various cooling holes therein which are substantially smaller in diameter than the dust holes.
Over extended operation of the airfoil, a crack may develop in the tip thereof and propagate radially inwardly. If the crack breaches the internal cooling channels, the cooling air may leak therethrough and adversely affect the intended cooling of the blade. For example, the airfoil may include a multi-pass serpentine cooling circuit which extends radially upwardly and downwardly in serpentine passes, with the cooling air being channeled therethrough cooling the airfoil and increasing in temperature along the length of the serpentine circuit. If the tip crack reaches the serpentine circuit at one of its passes, the downstream passes may be deprived of a portion of the cooling air intended therefor which can cause an increase in operating temperature of the airfoil and accelerate propagation of the tip crack leading to an undesirably shortened blade life.
Accordingly, it is desired to provide a crack arresting feature in the airfoil which does not interfere or degrade effective cooling of the blade for enhancing blade life.